Microwave shows F15 and may not heat or may shut down when starting a cook cycle.

Safety First: The high-voltage system in a microwave is extremely dangerous. Unplug the unit and do not attempt to discharge or test the high-voltage capacitor unless you are trained and equipped. This repair is best left to a qualified technician.

• Basic checks only: As a homeowner, limit yourself to verifying that the unit is properly ventilated and that no obvious burning smell or smoke is present.
• Professional diagnosis: A technician will test the high-voltage capacitor, transformer, magnetron, and HV diode with appropriate tools and safety procedures.
• Component replacement: Depending on test results, the technician will replace the failed high-voltage component(s). Often, a shorted magnetron or capacitor is the root cause.